1. Field of the Invention
The present invention relates to a tunnel junction film consisting of a free layer, a barrier layer, and a pinned layer for reading an information signal from a magnetic recording medium and in particular, to a production method of a magnetoresistive head having a tunnel junction film.
2. Description of the Related Art
Conventionally, there has been disclosed a magnetic reading converter called a magnetoresistive (MR) sensor or head. It is known that the MR sensor or head can read data from a magnetic surface with a great linear density. The MR sensor detects a magnetic signal via xe2x80x98a resistance change as a function of direction of magnetic flux intensityxe2x80x99 which is detected by a reading element. Such a conventional MR sensor operates according to an anisotropic magnetic resistance (AMR) effect. The AMR effect is that a resistance component of a reading element changes in proportion of a square of cosine of the angle between a magnetization direction and the direction of a current detected. The AMR effect is detailed in D. A. Thompson xe2x80x9cMemory, Storage, and Related Applicationsxe2x80x9d IEEE Trans. on Mag. MAG-11, p. 1039 (1975). A magnetic head using the AMR effect normally applies a longitudinal bias so as to suppress the Barkhausen noise. This longitudinal bias is often applied using an anti-ferromagnetic material such as FeMn, NiMn, and nickel oxide.
Recently, there is a description on more remarkable magnetoresistivity based on a conductive electron spin dependent transfer between magnetic layers via a non-magnetic layer and an accompanying spin dependent scattering on the boundary plane. This magnetoresistivity is called by various names such as xe2x80x9cgiant magnetoresistivityxe2x80x9d and xe2x80x9cspin bulb effectxe2x80x9d. Such a magnetic sensor is made from an appropriate material and exhibits an improved sensitivity and greater resistance change than the sensor using AMR. In this type of MR sensor, within-plane resistance of ferromagnetic layers separated by a non-magnetic layer changes in proportion to cosine of the angle between the magnetization directions of the two layers.
Japanese Patent Publication No. 2-61572 discloses a layered magnetic structure bringing about a high MR change caused by anti-parallel arrangement of magnetization in the magnetic layers. In this Publication, as a material which can be used in the layered structure, there are exemplified ferromagnetic transition metals and alloys. Moreover, it is disclosed that one of at least two ferromagnetic layers separated by an intermediate layer is provided with a pinning layer, which is preferably made from FeMn.
Japanese Patent Publication No. 4-103014 discloses a ferromagnetic tunnel junction element having an intermediate layer inserted between ferromagnetic layers, to form a multi-layered film wherein a bias magnetic field from an anti-ferromagnetic layer is applied to at least one of the ferromagnetic layers, so as to constitute a ferromagnetic tunnel junction film.
A shield type MR head using the ferromagnetic tunnel junction film (MTJ film) basically consists of a free layer, a barrier layer, and a pinned layer. However, since a barrier layer is an insulation layer and the free layer and the pinned layer are metal layers, the combination of the free layer, the barrier layer, and the pinned layer serves like a capacitor, and electric charges are easily accumulated in the free layer and the pinned layer. For this, in a production procedure, if too much electric charge is accumulated in the free layer and the pinned layer, a great voltage is applied to both surfaces of the barrier layer and the barrier layer is often destroyed by discharge. The MTJ film shows a resistance change caused by polarization of the ferromagnetic layers at the both surfaces of the insulation layers. Accordingly, if the insulation destruction is caused and a current bypass is formed, almost no resistance change is generated in the MTJ film.
A recording/reproduction head using the MTJ film is produced according to a following procedure.
1) A lower shield is formed on a wafer.
2) A lower gap is formed.
3) A lower electrode is formed.
4) An MTJ film is formed.
5) A longitudinal bias is formed.
6) An upper electrode is formed.
7) An upper gap is formed.
8) A common pole is formed.
9) A yoke is formed.
10) A coil is formed.
11) An insulation layer is formed.
12) An upper pole is formed.
13) A terminal is formed.
14) An ABS is lapped.
Here, photoresist (PR) process is often used in formation of the lower shield, the lower gap, lower electrode, the MTJ film, the longitudinal bias, the upper electrode, the upper gap, the common pole, the yoke, the coil, the insulation layer, and the upper pole. In the PR process, baking is performed such as pre-bake, positive-negative reverse baking, post-baking, and the like. These processes are performed in a dry atmosphere of a high temperature. Accordingly, friction between the wafer and the air often causes static electricity. The static electricity after the MTJ film formation leads to the electrostatic destruction (ESD) of the barrier layer. Moreover, in the aforementioned production steps, milling is performed after PR formation. Ion generation during milling often charges up the free layer and the pinned layer of the MTJ film, causing electrostatic destruction of the barrier layer.
Thus, electric charge generated during the production of an MR head destroys the barrier layer of the MTJ film. Accordingly, when the aforementioned production steps are complete, the yield of the MR head is significantly reduced.
It is therefore an object of the present invention to provide a magnetoresistive (MR) head production method in which insulation destruction is prevented during the production of a barrier layer of the tunnel junction film, so that the production yield is improved.
The MR head production method according to the present invention is a method for producing an MR head having a tunnel junction film consisting of a free layer, a barrier layer, and a pinned layer, the method comprising: a first step of forming a resistance value between the free layer and the pinned layer smaller than a resistance value when used as the MR head; and a second step of increasing the resistance value formed in the first step, to a resistance value when used as the MR head.
In other words, in a production process of an MR head using the tunnel junction film basically consisting of a free layer, a barrier layer, and a pinned layer, the resistance between the free layer and the pinned layer is reduced beforehand and increased afterward up to a resistance value necessary when actually used. When the resistance between the free layer and the pinned layer is low, current flows easily and charge up is suppressed, thus preventing the insulation destruction of the barrier layer. And the resistance between the free layer and the pinned layer is increased afterward so as to serve as a reproduction head.